High-purity composite materials, methods of making high-purity composite materials, and methods of using high-purity composite materials

ABSTRACT

A composite filter aid may include acid-washed diatomaceous earth and a low extractable metal mineral. A method for making a composite material may include blending an acid-washed diatomaceous earth and a low extractable metal mineral, adding a binder to the blended diatomaceous earth and low extractable metal mineral, and forming the composite material from the acid-washed diatomaceous earth, the low extractable metal mineral, and the binder. A method for filtering a liquid may include providing a liquid for filtering and filtering the liquid through a composite filter aid that includes an acid-washed diatomaceous earth and a low extractable metal mineral.

CLAIM FOR PRIORITY

This PCT International Application claims the benefit of priority of U.S. Provisional Patent Application No. 62/102,897, filed Jan. 13, 2015, the subject matter of which is incorporated herein by reference in its entirety.

FIELD OF THE DESCRIPTION

This disclosure is related to high-purity composite materials, methods for making high-purity composite filter aid materials, and methods for using high-purity composite materials. More particularly, this disclosure relates to high-purity composite materials that may be used in filtration applications, and methods for making and using such high-purity composite materials.

BACKGROUND

In many filtration applications, a filtration device may include a filter element, such as a septum, and a filter-aid material. The filter element may be of any form such that it may support a filter-aid material. For example, the filter element may include a cylindrical tube or wafer-like structure covered with a plastic or metal fabric of sufficiently fine weave. The filter element may be a porous structure with a filter element void to allow material of a certain size to pass through the filtration device. The filter-aid material may include one or more filtration components, which, for example, may be inorganic powders or organic fibrous materials. Such a filter-aid material may be used in combination with a filter element to enhance filtration performance.

For example, the filter-aid material may initially be applied to a septum of a filter element in a process known as “pre-coating.” Pre-coating may generally involve mixing a slurry of water and filter-aid material, and introducing the slurry into a stream flowing through the septum. During this process, a thin layer, such as, for example, about 1.5 mm to about 3.0 mm, of filter-aid material may eventually be deposited on the septum, thus forming the filtration device.

During filtration of a fluid, various insoluble particles in the fluid may become trapped by the filter-aid material. The combined layers of filter-aid material and particles and/or constituents to be removed accumulate on the surface of the septum. Those combined layers are known as “filter cake.” As more and more particles and/or constituents are deposited on the filter cake, the filter cake may become saturated with debris to the point where fluid is no longer able to pass through the septum.

To combat this situation, a process known as “body feeding” may be used. Body feeding is the process of introducing additional filter-aid material into the fluid to be filtered before the fluid reaches the filter cake. The filter-aid material will follow the path of the unfiltered fluid and will eventually reach the filter cake. Upon reaching the filter cake, the added filter-aid material will bind to the cake in a similar manner to how the filter-aid material is bound to the septum during the pre-coating process. The additional layer of filter-aid material may cause the filter cake to swell and thicken, and may increase the capacity of the filter cake to entrap additional debris. The filter aid typically has an open porous structure, which maintains an open structure in the filter cake, thus ensuring continued permeability of the filter cake.

In the field of fluid filtration, diatomaceous earth, also known as diatomite or “DE,” may be employed as a filter aid, and methods of particle separation from fluids may employ diatomaceous earth products as filter aids. The intricate and porous structure unique to diatomaceous earth may, in some instances, be effective for the physical entrapment of particles in filtration processes. It is known to employ diatomaceous earth products to improve the clarity of fluids that exhibit “turbidity” or contain suspended particles or particulate matter. “Turbidity” is the cloudiness or haziness of a fluid, where the haze may be caused by individual particles that are suspended in the fluid. Materials that may cause a fluid to be turbid include, for example, clay, silt, organic matter, inorganic matter, and microscopic organisms.

Diatomaceous earth may be used in various aspects of filtration. For example, as a part of pre-coating, diatomaceous earth products may be applied to a filter septum to assist in achieving, for example, any one or more of: protection of the septum, improvement in clarity, and expediting of filter cake removal. As a part of body feeding, diatomaceous earth may be added directly to a fluid being filtered to assist in achieving, for example, either or both of: increasing flow rate and extending of the filtration cycle. Depending on the requirements of the specific separation process, diatomaceous earth may be used in multiple stages including, but not limited to, in a pre-coating stage and in a body feeding stage.

Known diatomaceous earth products may suffer from any number of attributes that make them inappropriate for filtration use, cause them to be less desirable, or cause them to have poor or improvable performance in a particular application, for instance in filtering applications. For example, known diatomaceous earth products may have a high soluble metal content, a high impurity content, and low permeability. Other components used with the diatomaceous earth may also increase the soluble metal content, rendering them inappropriate for use in food and beverage applications. Thus, it may be desirable to improve diatomaceous earth products such that they exhibit improved performance in a given application, such as lower impurity content, low soluble metal content, and/or higher permeability in filtration applications.

SUMMARY

In accordance with a first aspect, a composite filter aid may include an acid-washed diatomaceous earth and a low extractable metal mineral.

According to another aspect, the filter aid may have a permeability in a range from 0.1 to 20 darcys, such as, for example, from 0.1 to 10 darcys, from 0.1 to 5 darcys, or from 0.1 to 3 darcys.

According to another aspect, the acid-washed diatomaceous earth may be obtained from a freshwater source or a saltwater source.

According to still another aspect, the low extractable metal mineral may include at least one of perlite, pumice, volcanic ash, kaolin, smectite, mica, talc, shirasu, obsidian, pitchstone, rice hull ash, or combinations thereof. The low extractable metal mineral may include perlite, such as, for example, an expanded perlite, an unexpanded perlite, a milled expanded perlite, or an acid-washed perlite.

According to another aspect, the acid-washed diatomaceous earth may include an acid-washed calcined diatomaceous earth or an acid-washed flux calcined diatomaceous earth.

According to yet another aspect, the composite filter aid may include a binder. The binder may include at least one of an inorganic binder or an organic binder. For example, the binder may include at least one of a cellulose, polyethylene glycol (PEG), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), starch, Candalilla wax, a polyacrylate or related copolymer, a polydiallyldimethylammonium chloride polymer or copolymer, dextrin, lignosulfonate, sodium alginate, magnesium stearate, a silica binder, an alkali silica, or mixtures thereof. The binder may include an alkali silicate binder, such as, for example, sodium silicate or potassium silicate.

According to a further aspect, the composite filter aid may have a d₁₀ in a range from 3 to 30 microns, a d₅₀ in a range from 15 to 70 microns, and a d₉₀ in a range from 50 to 200 microns. The acid-washed diatomaceous earth may have a d₁₀ in a range from 3 to 20 microns, a d₅₀ in a range from 15 to 80 microns, and a d₉₀ in a range from 50 to 200 microns. The low extractable metal mineral may have a d₁₀ in a range from 3 to 30 microns, a d₅₀ in a range from 15 to 80 microns, and a d₉₀ in a range from 50 to 200 microns.

According to yet another aspect, a ratio of the acid-washed diatomaceous earth to the low extractable metal mineral may be in a range from 1:99 to 99:1 by weight. For example, the ratio of the acid-washed diatomaceous earth to the low extractable metal mineral may be in a range from 25:75 to 75:25 by weight.

According to a further aspect, the composite filter aid may have a BET surface area in a range from 5 m²/g to 50 m²/g. According to yet another aspect, the composite filter aid may have a median pore size in a range from 1 to 35 microns, and a surface area in a range from 5 to 40 m²/g. According to another aspect, the porosity (e.g., pore volume) of the composite filter aid may be in a range from 2 to 7 mL/g.

According to still another aspect, the composite filter aid may have a beer soluble iron content of less than 40 ppm, as measured by EBC. For example, the filter aid may have a beer soluble iron content of less than 20 ppm, as measured by EBC,

According to yet another aspect, the composite filter aid may have a cristobalite content of less than 20% by weight. For example, the composite filter aid may have a cristobalite content of less than 10% by weight, less than 6% by weight, or less than 1% by weight.

According to another aspect, the composite filter aid may have a wet density in a range from 5 to 25 lbs/ft³, such as, for example, from 10 to 15 lbs/ft³.

According to yet another aspect, a composite filter aid may include diatomaceous earth, perlite, and a binder, wherein the filter aid has a wet density less than 20 lbs/ft³.

According to some aspects, the low extractable metal mineral may include a low soluble metal content. According to some aspects, the low extractable metal mineral may include an acid-washed low extractable metal mineral.

According to still another aspect, a method for making a composite material may include blending an acid-washed diatomaceous earth and a low extractable metal mineral, adding a binder to the blended acid-washed diatomaceous earth and low extractable metal mineral, and forming the composite material from the acid-washed diatomaceous earth, the low extractable metal mineral, and the binder. According to another aspect, forming the composite material may include precipitating the binder to form the composite material.

According to another aspect, the method may further include dispersing the binder in water. For example, the method may further include dispersing the binder in water before adding the binder to the blended acid-washed diatomaceous earth and low extractable metal mineral. The method may further include mixing the binder and the blended acid-washed diatomaceous earth and low extractable metal mineral. The method may further include classifying the mixed binder and blended acid-washed diatomaceous earth and low extractable metal mineral. The method may further include drying the mixed binder and blended acid-washed diatomaceous earth and low extractable metal mineral. For example, the drying may include heating the mixed binder and blended acid-washed diatomaceous earth and low extractable metal mineral to a temperature in a range from 100° C. to 200° C. The method may further include, after drying the mixture, classifying the mixture. The method may further include, prior to blending the acid-washed diatomaceous earth and low extractable metal mineral, calcining the diatomaceous earth.

According to yet another aspect, a method for filtering a liquid may include using a composite filter aid and/or composite material. The composite filter aid and/or composite material may include an acid-washed diatomaceous earth and a low extractable metal mineral,

According to another aspect, the method may also include, prior to filtering the liquid, pre-coating a filter element with the composite filter aid and/or composite material. Providing the liquid may include adding the composite filter aid and/or composite material as a body feed in the liquid.

According to another aspect, the liquid may include a beverage, such as, for example, beer.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph depicting pressure versus filtration time for an exemplary filter aid.

FIG. 2 is a graph depicting turbidity versus filtration time for the exemplary filter aid shown in FIG. 1.

FIG. 3 is a graph depicting pressure versus filtration time for another exemplary filter aid.

FIG. 4 is a graph depicting turbidity versus filtration time for the exemplary filter aid shown in FIG. 3.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

According to some embodiments, a composite filter aid may include an acid-washed diatomaceous earth and a low extractable metal mineral. For example, the acid-washed diatomaceous earth and low extractable metal mineral may be blended and contacted with a binder solution, so that the blended diatomaceous earth and low extractable metal mineral co-agglomerate. The composite material may be used as, for example, a filter aid. The resulting filter aid may exhibit increased permeability and/or improved filtration performance, such as lower pressure rise with time at similar turbidity or lower bodyfeed usage at similar turbidity and pressure rise. While not wishing to be bound to a particular theory, it is believed that the co-agglomeration of acid-washed diatomaceous earth and low extractable metal mineral results in the diatomaceous earth and low extractable metal mineral particles attaching to one another to form larger particles relative to a blend of diatomaceous earth and low extractable metal mineral particles that has not been co-agglomerated.

According to some embodiments, the filter aid may have a permeability in a range from 0.1 to 20 darcys, such as, for example, from 0.1 to 10 darcys, from 0.1 to 5 darcys, or from 0.1 to 3 darcys.

According to some embodiments, the acid-washed diatomaceous earth may be obtained from a freshwater source or a saltwater source.

According to some embodiments, the low extractable metal mineral may include at least one of perlite, pumice, volcanic ash, kaolin, smectite, mica, talc, shirasu, obsidian, pitchstone, rice hull ash, or combinations thereof. The low extractable metal mineral may include perlite, such as, for example, an expanded perlite, an unexpanded perlite, a milled expanded perlite, or an acid-washed perlite.

According to some embodiments, the acid-washed diatomaceous earth may include an acid-washed calcined diatomaceous earth or an acid-washed flux calcined diatomaceous earth.

According to some embodiments, the composite filter aid may include a binder. The binder may include at least one of an inorganic binder or an organic binder. For example, the binder may include at least one of a cellulose, polyethylene glycol (PEG), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), starch, Candalilla wax, a polyacrylate or related copolymer, a polydiallyldimethylammonium chloride polymer or copolymer, dextrin, lignosulfonate, sodium alginate, magnesium stearate, a silica binder, an alkali silica, or mixtures thereof. The binder may include an alkali silicate binder, such as, for example, sodium silicate or potassium silicate.

According to some embodiments, the composite filter aid may have a d₁₀ in a range from 5 to 30 microns. According to some embodiments, the composite filter aid may have a d₅₀ in a range from 15 to 70 microns. According to some embodiments, the composite filter aid may have a d₉₀ in a range from 50 to 200 microns.

According to some embodiments, the acid-washed diatomaceous earth may have a d₁₀ in a range from 3 to 15 microns. According to some embodiments, the acid-washed diatomaceous earth may have a d₅₀ in a range from 10 to 70 microns. According to some embodiments, the acid-washed diatomaceous earth may have a d₉₀ in a range from 30 to 130 microns.

According to some embodiments, the low extractable metal mineral may have a d₁₀ in a range from 3 to 30 microns. According to some embodiments, the low extractable metal mineral may have a d₅₀ in a range from 10 to 80 microns. According to some embodiments, the low extractable metal mineral may have a d₉₀ in a range from 30 to 150 microns.

According to some embodiments, a ratio of the acid-washed diatomaceous earth to the low extractable metal mineral may be in a range from 1:99 to 99:1 by weight. For example, the ratio of the acid-washed diatomaceous earth to the low extractable metal mineral may be in a range from 20:80 to 80:20, from 25:75 to 75:25, from 30:70 to 70:30, or from 40:60 to 60:40 by weight. According to some embodiments, the ratio of the acid-washed diatomaceous earth to the low extractable metal mineral may be 50:50 by weight.

According to some embodiments, the composite filter aid may have a BET surface area in a range from 1 m²/g to 50 m²/g.

According to some embodiments, the composite filter aid has a median pore size in a range from 1 to 35 microns, such as, for example, from 1 to 20 microns, from 1 to 10 microns, from 3 to 10 microns, or from 3 to 5 microns.

According to some embodiments, the composite filter aid may have a BET surface area in a range from 1 to 50 m²/g.

According to some embodiments, the pore volume of the composite filter aid may range from 2 to 7 mL/g.

According to some embodiments, the composite filter aid has a beer soluble iron content of less than 50 ppm, as measured by EBC. For example, the filter aid has a beer soluble iron content of less than 40 ppm, less than 30 ppm, less than 20 ppm, or less than 10 ppm, as measured by EBC.

According to some embodiments, the composite filter aid has a beer soluble calcium content of less than 200 ppm, as measured by EBC. For example, the filter aid has a beer soluble calcium content of less than 150 ppm, less than 100 ppm, less than 50 ppm, less than 30 ppm, or less than 15 ppm, as measured by EBC.

According to some embodiments, the composite filter aid has a beer soluble aluminum content of less than 30 ppm, as measured by EBC. For example, the filter aid has a beer soluble aluminum content of less than 20 ppm, less than 15 ppm, or less than 10 ppm, as measured by EBC.

According to some embodiments, the composite filter aid has a beer soluble arsenic content of less than 5 ppm, as measured by EBC. For example, the filter aid has a beer soluble arsenic content of less than 2 ppm, less than 1 ppm, less than 0.5 ppm, or less than 0.2 ppm, as measured by EBC.

According to some embodiments, the composite filter aid (e.g., the diatomaceous earth component) has an acid-soluble iron content of less than 100 mg/kg, as measured by Food Chemicals Codex (FCC) method. For example, the filter aid has an acid-soluble iron content of less than 50 mg/kg, less than 40 mg/kg, or less than 30 mg/kg, as measured by FCC.

According to some embodiments, the composite filter aid (e.g., the diatomaceous earth component) has an acid-soluble iron content of less than 100 parts per million (ppm), as measured by Food Chemicals Codex (FCC) method. For example, the filter aid has an acid-soluble iron content of less than 70 ppm, less than 50 ppm, less than 40 ppm, less than 30 ppm, less than 20 ppm, or less than 10 ppm, as measured by FCC.

According to some embodiments, the composite filteraid (e.g., the diatomaceous earth component) has an acid-soluble aluminum content of less than 280 mg/kg, as measured by FCC. For example, the filter aid has an acid-soluble aluminum content of less than 200 mg/kg, less than 100 mg/kg, or less than 80 mg/kg, as measured by FCC.

According to some embodiments, the composite filter aid (e.g., the diatomaceous earth component) has an acid-soluble aluminum content of less than 280 ppm, as measured by FCC. For example, the filter aid has an acid-soluble aluminum content of less than 200 ppm, less than 100 ppm, less than 80 ppm, less than 50 ppm, less than 30 ppm, less than 20 ppm, less than 15 ppm, or less than 10 ppm, as measured by FCC.

According to some embodiments, the composite filter aid (e.g., the diatomaceous earth component) has an acid-soluble arsenic content of less than 5 mg/kg, as measured by FCC. For example, the filter aid has an acid-soluble arsenic content of less than 2 mg/kg, less than 1 mg/kg, or less than 0.5 mg/kg, as measured by FCC.

According to some embodiments, the composite filter aid (e.g., the diatomaceous earth component) has an acid-soluble arsenic content of less than 10 ppm, as measured by FCC. For example, the filter aid has an acid-soluble arsenic content of less than 5 ppm, less than 2 ppm, less than 1 ppm, less than 0.5 ppm, or less than 0.2 ppm, as measured by FCC.

According to some embodiments, the composite filter aid (e.g., the diatomaceous earth component) has an acid-soluble copper content of less than 5 mg/kg, as measured by FCC. For example, the filter aid has an acid-soluble copper content of less than 2 mg/kg, less than 1.5 mg/kg, or less than 1 mg/kg, as measured by FCC.

According to some embodiments, the composite filter aid (e.g., the diatomaceous earth component) has an acid-soluble copper content of less than 5 ppm, as measured by FCC. For example, the filter aid has an acid-soluble copper content of less than 2 ppm, less than 1.5 ppm, or less than 1 ppm, as measured by FCC.

According to some embodiments, the composite filter aid (e.g., the diatomaceous earth component) has an acid-soluble calcium content of less than 200 mg/kg, as measured by FCC. For example, the filter aid has an acid-soluble calcium content of less than 150 mg/kg, less than 100 mg/kg, less than 50 mg/kg, or less than 30 mg/kg, as measured by FCC.

According to some embodiments, the composite filter aid (e.g., the diatomaceous earth component) has an acid-soluble calcium content of less than 200 ppm, as measured by FCC. For example, the filter aid has an acid-soluble calcium content of less than 150 ppm, less than 100 ppm, less than 50 ppm, or less than 30 ppm, as measured by FCC.

According to some embodiments, the composite filter aid (e.g., the diatomaceous earth component) has an acid-soluble lead content of less than 1 mg/kg, as measured by FCC. For example, the filter aid has an acid-soluble lead content of less than 0.5 mg/kg, less than 0.2 mg/kg, or less than 0.1 mg/kg, as measured by FCC.

According to some embodiments, the composite filter aid (e.g., the diatomaceous earth component) has a cristobalite content of less than 20% by weight. For example, the composite filter aid has a cristobalite content of less than 10% by weight, less than 6% by weight, or less than 1% by weight.

According to some embodiments, the composite filter aid has a wet density in a range from 5 to 30 lbs/ft³, such as, for example, from 10 to 15 lbs/ft³. According to some embodiments, the composite filter aid has a wet density less than or equal to 20 lbs/ft³, less than or equal to 15 lbs/ft³, or less than or equal to 10 lbs/ft³.

According to some embodiments, a composite filter aid includes acid-washed diatomaceous earth, a low extractable metal mineral, and a binder, wherein the filter aid has a wet density less than 15 lbs/ft³.

According to some embodiments, a method for making a composite material includes blending an acid-washed diatomaceous earth and a low extractable metal mineral, adding a binder to the blended acid-washed diatomaceous earth and low extractable metal mineral, and forming the composite material from the acid-washed diatomaceous earth, the low extractable metal mineral, and the binder. According to another aspect, forming the composite material may include precipitating the binder to form the composite material.

The method may further include dispersing the binder in water. For example, the method may further include dispersing the binder in water before adding the binder to the blended acid-washed diatomaceous earth and low extractable metal mineral. The method may further include mixing the binder and the blended acid-washed diatomaceous earth and low extractable metal mineral. The method may further include classifying the mixed binder and blended acid-washed diatomaceous earth and low extractable metal mineral. The method may further include drying the mixed binder and blended acid-washed diatomaceous earth and low extractable metal mineral. For example, the drying may include heating the mixed binder and blended acid-washed diatomaceous earth and low extractable metal mineral to a temperature in a range from 100° C. to 200° C. The method may further include, after drying the mixture, classifying the mixture. The method may further include, prior to blending the acid-washed diatomaceous earth and low extractable metal mineral, calcining the diatomaceous earth.

According to some embodiments, a method for filtering a liquid includes using a composite filter aid and/or composite material. The composite filter aid and/or composite material may include an acid-washed diatomaceous earth and a low extractable metal mineral.

According to some embodiments, the method may also include, prior to filtering the liquid, pre-coating a filter structure with the composite filter aid and/or composite material. Providing the liquid may include adding the composite filter aid and/or composite material as a body feed in the liquid.

According to some embodiments, the liquid may include a beverage. According to some embodiments, the beverage may include beer, wine, juice, or water,

Diatomaceous Earth

Diatomaceous earth products may be obtained from diatomaceous earth (also called “DE” or “diatomite”), which is generally known as a sediment-enriched in biogenic silica (i.e., silica produced or brought about by living organisms) in the form of siliceous skeletons (frustules) of diatoms. Diatoms are a diverse array of microscopic, single-celled, golden-brown algae generally of the class Bacillariophyceae that possess an ornate siliceous skeleton of varied and intricate structures including two valves that, in the living diatom, fit together much like a pill box.

Diatomaceous earth may form from the remains of water-borne diatoms and, therefore, diatomaceous earth deposits may be found close to either current or former bodies of water. Those deposits are generally divided into two categories based on source: freshwater and saltwater. Freshwater diatomaceous earth is generally mined from dry lakebeds and may be characterized as having a low crystalline silica content and a high iron content. In contrast, saltwater diatomaceous earth is generally extracted from oceanic areas and may be characterized as having a high crystalline silica content and a low iron content.

Processes for preparing the diatomaceous earth products may include at least one natural diatomaceous earth as a starting material. For example, the term “natural diatomaceous earth” includes any diatomaceous earth material that has not been subjected to thermal treatment (e.g., calcination) sufficient to induce formation of greater than 1% cristobalite. “Natural diatomaceous earth” may also include diatomaceous earth including uncalcined diatomaceous earth. In some embodiments, the diatomaceous earth may be obtained from a saltwater source. In some embodiments, the diatomaceous earth may be obtained from a freshwater source. In further embodiments, the diatomaceous earth is any diatomaceous earth material that may be capable of use in composite material such as a composite filter aid, either in its natural form or after subjecting the material to one or more processing steps. In some embodiments, the diatomaceous earth is any diatomaceous earth material that has not been subjected to at least one thermal treatment. In still other embodiments, the diatomaceous earth is any diatomaceous earth material that has not been subjected to calcination. The average particle size for the diatomaceous earth may be in a range from 3 to 200 microns. The BET surface area of the diatomaceous earth may be in a range from 1 to 80 m²/g. The pore volume of the diatomaceous earth may range from 1 to 10 mL/g with median pore size ranging from 1 to 20 microns.

As stated earlier, diatomaceous earth is, in general, a sedimentary biogenic silica deposit including the fossilized skeletons of diatoms, one-celled algae-like plants that accumulate in marine or fresh water environments. Honeycomb silica structures generally give diatomaceous earth useful characteristics such as absorptive capacity and surface area, chemical stability, and low-bulk density. In some embodiments, diatomaceous earth includes about 90% SiO₂ mixed with other substances. In some embodiments, diatomaceous earth includes about 90% SiO₂, plus various metal oxides, such as, but not limited to, Al, Fe, Ca, and Mg oxides.

Diatomaceous earth may have any of various appropriate forms now known to the skilled artisan or hereafter discovered. In some embodiments, the diatomaceous earth may undergo one or more of a milling, drying, or air classifying process. In some embodiments, the diatomaceous earth may be subjected to at least one chemical modification process. An example of a chemical modification process is silanization, but other chemical modification processes are contemplated. Silanization may be used to render the surfaces of the at least one diatomaceous earth either more hydrophobic or hydrophilic using the methods appropriate for silicate minerals. Such physical and chemical modification processes may occur before or after an acid-washing step.

Low Extractable Metal Mineral

The low extractable metal mineral may include a mineral material having a low extractable metal content. For example, the low extractable metal mineral may include one or more of perlite, pumice, volcanic ash, kaolin, smectite, mica, talc, shirasu, obsidian, pitchstone, and rice hull ash.

According to some embodiments, the low extractable metal mineral may include a “natural glass” or “volcanic glass.” Several types of natural glasses include, for example, perlite, pumice, pumicite, shirasu, obsidian, pitchstone, and volcanic ash. Prior to processing, perlite may be gray to green in color with abundant spherical cracks that cause it to break into small pearl-like masses. Pumice is a lightweight glassy vesicular rock. Obsidian may be dark in color with a vitreous luster and a characteristic conchoidal fracture. Pitchstone has a waxy resinous luster and may be brown, green, or gray. Volcanic ash, sometimes referred to as “tuff” when in consolidated form, includes small particles or fragments that may be in glassy form. According to some embodiments, the low extractable metal mineral may be chemically equivalent to rhyolite, trachyte, dacite, andesite, latite, or basalt.

The term “obsidian” is generally applied to large numbers of natural glasses that are rich in silica. Obsidian glasses may be classified into subcategories according to their silica content, with rhyolitic obsidians (containing typically about 73% SiO₂ by weight) being the most common.

Perlite is a hydrated material that may contain, for example, about 72 to about 75% SiO₂, about 12 to about 14% Al₂O₃, about 0.5 to about 2% Fe₂O₃, about 3 to about 5% Na₂O, about 4 to about 5% K₂O, about 0.4 to about 1.5% CaO (by weight), and small amounts of other metallic elements. In some embodiments, perlite may be distinguished by a relatively higher content (such as about 2 to about 5% by weight) of chemically-bonded water, the presence of a vitreous, pearly luster, and characteristic concentric or arcuate onion skin-like (i.e., perlitic) fractures.

Perlite products may be prepared by milling and thermal expansion, and may possess unique physical properties such as high porosity, low bulk density, and chemical inertness. Average particle size for the milled expanded perlite may be in a range from 3 to 200 microns. Pore volume for milled expanded perlite may be in a range from 1 to 10 mL/g with median pore size from 1 to 20 microns. According to some embodiments, the perlite may include expanded perlite. According to some embodiments, the perlite may include unexpanded perlite. According to some embodiments, the perlite may include milled expanded perlite.

Pumice is a mineral composition characterized by a mesoporous structure (e.g., having pores or vesicles with a size up to about 1 mm). The porous nature of pumice gives it a very low apparent density, in many cases allowing it to float on the surface of water. Most commercial pumice contains from about 60% to about 70% SiO₂ by weight. Pumice may be processed by milling and classification, and products may be used as lightweight aggregates and also as abrasives, adsorbents, and fillers. Unexpanded pumice and thermally-expanded pumice may also be used as filtration components.

Acid Washing

The diatomaceous earth may be an acid-washed diatomaceous earth. According to some embodiments, the low extractable metal mineral may include an acid-washed low extractable metal mineral.

The acid washing step may include washing the diatomaceous earth and/or low extractable metal mineral with at least one acid. The at least one acid may include a mineral acid, such as, for example, sulfuric acid (H₂SO₄), hydrochloric acid (HCl), phosphoric acid (H₃PO₄), and nitric acid (HNO₃). The at least one acid may include an organic acid, such as, for example, citric acid (C₆H₈O₇) or acetic acid (CH₃COOH). As used in this disclosure, the acid washing may also be referred to as “acid leaching” or “acid extracting.” Without wishing to be bound by a particular theory, it is believed that the acid washing step extracts or leaches metal-containing compounds from the diatomaceous earth and/or low extractable metal mineral, thereby increasing the relative amount of silica (SiO₂) or other non-metallic components in the composition.

According to some embodiments, the acid washing step may be performed using an acid solution having an acid strength in a range from about 0.1 M to about 2 M, such as, for example, in a range from about 0.1 M to about 1M, from about 1 M to about 2 M, from about 0.5 M to about 1M, or from about 0.5 M to about 2 M. According to some embodiments, the solid content in the acid solution can range from about 5% to about 20%, such as from about 5% to about 15%, about 5% to about 10%, from about 10% to about 20%, or from about 15% to about 20%.

According to some embodiments, the acid washing step may occur at a temperature in a range from about ambient room temperature (about 20° C.) to about 200° C., such as, for example from about 20° C. to about 100° C., or from about 50° C. to about 100° C. According to some embodiments, the acid washing can be performed under ambient pressure. According to other embodiments, the acid washing can be performed under a pressure in a range from about ambient pressure to about 200 psi, such as, for example, from about 20 psi to about 200 psi, from about 50 psi to about 200 psi, or from about 20 psi to about 100 psi.

According to some embodiments, the acid washing step can be carried out for a time or duration in a range from about 10 minutes to about 120 minutes, such as, for example, from about 20 minutes to about 60 minutes, from about 30 minutes to about 60 minutes, from about 30 minutes to about 120 minutes, or from about 60 minutes to about 120 minutes. According to some embodiments, the acid washing step may include a step of rinsing the acid from the diatomaceous earth. The rinsing step may include, for example, more than one rinse with water, such as 1 to 3 rinses with water. According to some embodiments, the rinsing may be sufficient to increase the pH of the diatomaceous earth to a pH of at least about 5.0, such as, for example, at least about 5.5, at least about 6.0, at least about 6.5, or at least about 7.0. According to some embodiments, the rinses may be done at an elevated temperature (relative to ambient), such as, for example, at a temperature of at least about 30° C., at least about 40° C., or at least about 50° C.

According to some embodiments, a thermal processing step, such as, for example, a calcining step, may be carried out prior to the acid washing step. According to some embodiments, the acid washing step occurs prior to the thermal processing step. According to some embodiments, the calcining may include flux-calcining the diatomaceous earth or low extractable metal mineral,

When diatomaceous earth or low extractable metal mineral products are used in filters and/or food-related applications, metals and metal ions may become soluble. For example, acids may solubilize metal ions contained in various oxides or chemical compounds of the diatomaceous earth or mineral. Certain soluble metals, such as arsenic and lead, are undesirable, and high soluble concentrations of these metals may create health concerns when solubilized in high concentrations. Acid washing may reduce the solubility of undesirable metals by leaching the metals away during the wash. This reduction in soluble metals may improve the compatibility of the diatomaceous earth for use in filter applications or food-related applications. Unless described otherwise in this disclosure, “acid-soluble” or “soluble” metals may also be referred to herein as “extractable” metals.

Acid solubility may be measured by the Food Chemical Codex (FCC) method, for example, using a FISSON 1310+ ICP spectrometer.

According to some embodiments, the acid-washed diatomaceous earth may include less than or equal to about 10 mg/kg acid-soluble arsenic, less than or equal to about 5 mg/kg acid-soluble arsenic, less than or equal to about 1 mg/kg acid-soluble arsenic, such as, for example, less than or equal to about 0.8 mg/kg acid-soluble arsenic, less than or equal to about 0.7 mg/kg acid-soluble arsenic, less than or equal to about 0.6 mg/kg acid-soluble arsenic, less than or equal to about 0.5 mg/kg acid-soluble arsenic, less than or equal to about 0.4 mg/kg acid-soluble arsenic, less than or equal to about 0.3 mg/kg acid-soluble arsenic, less than or equal to about 0.2 mg/kg acid-soluble arsenic, or less than or equal to about 0.1 mg/kg acid-soluble arsenic. According to some embodiments, the acid-soluble arsenic may be at or below the detection limit of the instrument, which may generally be less than 0.1 mg/kg acid-soluble arsenic or 0.0 mg/kg acid-soluble arsenic.

According to some embodiments, the acid-washed diatomaceous earth may include an acid-soluble arsenic content of less than 10 ppm, as measured by FCC. For example, the acid-washed diatomaceous earth has an acid-soluble arsenic content of less than 5 ppm, less than 2 ppm, less than 1 ppm, less than 0.5 ppm, or less than 0.2 ppm, as measured by FCC.

According to some embodiments, the acid-washed diatomaceous earth may include less than or equal to about 1 mg/kg acid-soluble lead. For example, the diatomaceous earth may include less than or equal to about 0.8 mg/kg acid-soluble lead, less than or equal to about 0.7 mg/kg acid-soluble lead, less than or equal to about 0.6 mg/kg acid-soluble lead, less than or equal to about 0.5 mg/kg acid-soluble lead, less than or equal to about 0.4 mg/kg acid-soluble lead, less than or equal to about 0.3 mg/kg acid-soluble lead, less than or equal to about 0.2 mg/kg acid-soluble lead, or less than or equal to about 0.1 mg/kg acid-soluble lead. According to some embodiments, the acid-soluble lead may be at or below the detection limit of the instrument, which may generally be less than 0.1 mg/kg acid-soluble lead or 0.0 mg/kg acid-soluble lead.

According to some embodiments, the acid-washed diatomaceous earth may include less than or equal to about 100 mg/kg acid-soluble aluminum. For example, the diatomaceous earth may include less than or equal to about 70 mg/kg acid-soluble aluminum, less than or equal to about 60 mg/kg acid-soluble aluminum, less than or equal to about 50 mg/kg acid-soluble aluminum, less than or equal to about 40 mg/kg acid-soluble aluminum, less than or equal to about 30 mg/kg acid-soluble aluminum, less than or equal to about 20 mg/kg acid-soluble aluminum, less than or equal to about 15 mg/kg acid-soluble aluminum, less than or equal to about 10 mg/kg acid-soluble aluminum, less than or equal to about 5 mg/kg acid-soluble aluminum, or less than or equal to about 3 mg/kg acid-soluble aluminum.

According to some embodiments, the acid-washed diatomaceous earth may include an acid-soluble aluminum content of less than 280 ppm, as measured by FCC. For example, the acid-washed diatomaceous earth has an acid-soluble aluminum content of less than 200 ppm, less than 100 ppm, less than 80 ppm, less than 50 ppm, less than 30 ppm, less than 20 ppm, less than 15 ppm, or less than 10 ppm, as measured by FCC.

According to some embodiments, the acid-washed diatomaceous earth may include less than or equal to about 800 mg/kg acid-soluble calcium, such as, for example, less than or equal to about 500 mg/kg acid-soluble calcium, less than or equal to about 400 mg/kg acid-soluble calcium, less than or equal to about 300 mg/kg acid-soluble calcium, less than or equal to about 200 mg/kg acid-soluble calcium, less than or equal to about 150 mg/kg acid-soluble calcium, less than or equal to about 100 mg/kg acid-soluble calcium, less than or equal to about 75 mg/kg acid-soluble calcium, or less than or equal to about 50 mg/kg acid-soluble calcium.

According to some embodiments, the acid-washed diatomaceous earth may include an acid-soluble calcium content of less than 200 ppm, as measured by FCC. For example, the acid-washed diatomaceous earth has an acid-soluble calcium content of less than 150 ppm, less than 100 ppm, less than 50 ppm, or less than 30 ppm, as measured by FCC.

According to some embodiments, the acid-washed diatomaceous earth may include less than or equal to about 100 mg/kg acid-soluble iron, such as, for example, less than or equal to about 70 mg/kg acid-soluble iron, less than or equal to about 50 mg/kg acid-soluble iron, less than or equal to about 40 mg/kg acid-soluble iron, less than or equal to about 30 mg/kg acid-soluble iron, less than or equal to about 20 mg/kg acid-soluble iron, less than or equal to about 15 mg/kg acid-soluble iron, less than or equal to about 10 mg/kg acid-soluble iron, less than or equal to about 5 mg/kg acid-soluble iron, or less than or equal to about 3 mg/kg acid-soluble iron.

According to some embodiments, the acid-washed diatomaceous earth may have an acid-soluble iron content of less than 100 parts ppm, as measured by FCC method. For example, the acid-washed diatomaceous earth has an acid-soluble iron content of less than 70 ppm, less than 50 ppm, less than 40 ppm, less than 30 ppm, less than 20 ppm, or less than 10 ppm, as measured by FCC.

Binder

The diatomaceous earth and low extractable metal mineral may be subjected to at least one co-agglomeration with at least one binder.

According to some embodiments, the binder may include at least one of an inorganic binder or an organic binder. According to some embodiments, the binder may include an inorganic binder, such as an alkali silica binder, such as, for example, sodium silicate, potassium silicate, and mixtures thereof. According to some embodiments, the inorganic binder may include a cement, such as a calcium aluminate cement. In some embodiments, the inorganic binder may include a cement, such as a calcium phosphate cement, and/or a magnesium phosphate cement. In some embodiments, the inorganic binder may include a magnesium aluminum silicate clay. According to some embodiments, the binder may include a silicone or ethyl silicate.

According to some embodiments, the binder may include one or more organic binders or biopolymers. For example, the binder may include a cellulose, polyethylene glycol (PEG), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), starch, Candalilla wax, a polyacrylate or related copolymer (e.g., acrylic acid-acrylamide, etc.), a polydiallyldimethylammonium chloride polymer or copolymer (pDADMAC, etc.), dextrin, lignosulfonate, sodium alginate, magnesium stearate, and/or mixtures thereof.

Co-Agglomeration

Co-agglomeration of acid-washed diatomaceous earth, low extractable metal mineral, and binder may occur through any appropriate agglomeration processes known to the skilled artisan or hereafter discovered. For example, in some embodiments, co-agglomeration includes preparing at least one aqueous solution of the binder, and contacting the binder solution with a blend of the diatomaceous earth and low extractable metal mineral. One or more agglomerations may be performed, for example, in which multiple silica binders, multiple diatomaceous earths, and/or multiple low extractable metal mineral solutions are used.

In some embodiments, contacting includes mixing the binder solution with a blend of the diatomaceous earth and low extractable metal mineral. In some embodiments, the mixing includes agitation. In some embodiments, the blend of diatomaceous earth material, low extractable metal mineral, and binder solution are mixed sufficiently to at least substantially uniformly distribute the binder solution among the agglomeration points of contact of the diatomaceous earth and low extractable metal mineral. In some embodiments, the blend of the diatomaceous earth, low extractable metal mineral, and binder solution are mixed with sufficient agitation to at least substantially uniformly distribute the binder solution among the agglomeration points of contact of the blend of diatomaceous earth and low extractable metal mineral without damaging the structure of the diatomaceous earth or low extractable metal mineral. In some embodiments, the contacting includes-low-shear mixing.

In some embodiments, mixing occurs for about one hour. In other embodiments, mixing occurs for less than about one hour. In further embodiments, mixing occurs for about 30 minutes. In yet other embodiments, mixing occurs for about 20 minutes. In still further embodiments, mixing occurs for about 10 minutes.

In some embodiments, mixing occurs at about room temperature (i.e., from about 20° C. to about 23° C.). In other embodiments, mixing occurs at a temperature ranging from about 20° C. to about 50° C. In further embodiments, mixing occurs at a temperature ranging from about 30° C. to about 45° C. In still other embodiments, mixing occurs at a temperature ranging from about 35° C. to about 40° C.

According to some embodiments, contacting includes spraying the blend of the diatomaceous earth and the low extractable metal mineral with a binder solution. In some embodiments, the spraying is intermittent. In other embodiments, the spraying is continuous. In further embodiments, spraying includes mixing the blend of acid-washed diatomaceous earth and a low extractable metal mineral while spraying with the binder solution, for example, to expose different agglomeration points of contacts to the spray. In some embodiments, such mixing is intermittent. In other embodiments, such mixing is continuous.

In some embodiments, the binder is present in the binder solution in an amount from less than about 40% by weight, relative to the weight of the binder solution. In some embodiments, the binder may be in a range from about 1% to about 10% by weight of the solution. In further embodiments, the binder may be in a range from about 1% to about 5% by weight of the solution.

The aqueous solution of the binder may be prepared with water. In some embodiments, the water is deionized water. In some embodiments, the water is ultrapure water. In further embodiments, the water has been treated to remove or decrease the levels of metals, toxins, and/or other undesirable elements before it is contacted with the binder.

The amount of the aqueous solution contacted with the blend of acid-washed diatomaceous earth and low extractable metal mineral may range from about 0.25 parts to about 1,5 parts of aqueous solution to one part blend. In some embodiments, about 1 part aqueous solution is contacted with about 1 part blend of the diatomaceous earth and the low extractable metal mineral.

Classification

Before and/or after the agglomeration, the diatomaceous earth and/or the low extractable metal mineral may be subjected to at least one classification step. For example, before and/or after at least one heat treatment, the diatomaceous earth may, in some embodiments, be subjected to at least one classification step. In some embodiments, the particle size of the diatomaceous earth material and/or low extractable metal mineral is adjusted to a suitable or desired size using any one of several techniques well known in the art. In some embodiments, the diatomaceous earth material and/or low extractable metal mineral may be subjected to at least one mechanical separation to adjust the powder size distribution. Appropriate mechanical separation techniques are well known to the skilled artisan and include, but are not limited to, milling, grinding, screening, extrusion, triboelectric separation, liquid classification, aging, and air classification.

Heat Treatment

The diatomaceous earth, low extractable metal mineral, and/or co-agglomerated diatomaceous earth and low extractable metal mineral may be subjected to at least one heat treatment. Appropriate heat treatment processes are well-known to the skilled artisan, and include those now known or that may hereinafter be discovered. In some embodiments, the at least one heat treatment decreases the amount of organics and/or volatiles in the heat-treated diatomaceous earth and/or low extractable metal mineral. In some embodiments, the at least one heat treatment includes at least one calcination. In some embodiments, the at least one heat treatment includes at least one flux calcination. In some embodiments, the at least one heat treatment includes at least one roasting. A heat treatment may occur prior to acid washing of the diatomaceous earth and/or low extractable metal mineral.

Calcination may be conducted according to any appropriate process now known to the skilled artisan or hereafter discovered. In some embodiments, calcination is conducted at temperatures below the melting point of the diatomaceous earth and/or low extractable metal mineral. In some embodiments, calcination is conducted at a temperature ranging from about 600° C. to about 1100° C. In some embodiments, the calcination temperature ranges from about 600° C. to about 700° C. In some embodiments, the calcination temperature ranges from about 700° C. to about 800° C. In some embodiments, the calcination temperature ranges from about 800° C. to about 900° C. In some embodiments, the calcination temperature is chosen from the group consisting of about 600° C., about 700° C., about 800° C., about 900° C., about 1000° C., and about 1100° C. Heat treatment at a lower temperature may result in an energy savings over other processes for the preparation of diatomaceous earth and/or low extractable metal mineral.

Flux calcination includes conducting at least one calcination in the presence of at least one fluxing agent. Flux calcination may be conducted according to any appropriate process now known to the skilled artisan or hereafter discovered. In some embodiments, the at least one fluxing agent is any material now known to the skilled artisan or hereafter discovered that may act as a fluxing agent. In some embodiments, the at least one fluxing agent is a salt including at least one alkali metal. In some embodiments, the at least one fluxing agent is chosen from the group consisting of carbonate, silicate, chloride, and hydroxide salts. In other embodiments, the at least one fluxing agent is chosen from the group consisting of sodium, potassium, rubidium, and cesium salts. In still further embodiments, the at least one fluxing agent is chosen from the group consisting of sodium, potassium, rubidium, and cesium carbonate salts. According to some embodiments, residual metal content from a fluxing agent may be removed by acid washing.

Roasting may be conducted according to any appropriate process now known to the skilled artisan or hereafter discovered. In some embodiments, roasting is a calcination process conducted at a generally lower temperature that helps to avoid formation of crystalline silica in the diatomaceous earth and/or low extractable metal mineral. In some embodiments, roasting is conducted at a temperature in a range from about 450° C. to about 900° C. In some embodiments, the roasting temperature may be in a range from about 500° C. to about 800° C. In some embodiments, the roasting temperature may be in a range from about 600° C. to about 700° C. In some embodiments, the roasting temperature may be in a range from about 700° C. to about 900° C. In some embodiments, the roasting temperature is chosen from the group consisting of about 450° C., about 500° C., about 600° C., about 700° C., about 800° C., and about 900° C.

According to some embodiments, the diatomaceous earth and/or low extractable metal mineral may be subjected to at least one heat treatment, followed by co-agglomerating the heat treated diatomaceous earth and/or heat treated low extractable metal mineral with at least one binder.

Composite

A composite material, such as an agglomerated material made by the processes described herein, may have one or more beneficial attributes, making them desirable for use in one or a number of given applications. In some embodiments, the composite materials may be useful as part of a filter aid composition. In some embodiments, a filter aid composition may include at least one composite material. The composite material may have a low extractable metal content due to, for example, acid washing of the diatomaceous earth and, optionally, the low extractable metal mineral.

The composite filter aids disclosed herein may have a permeability suitable for use in a filter aid composition. Permeability may be measured by any appropriate measurement technique now known to the skilled artisan or hereafter discovered. Permeability is generally measured in darcy units or darcy, as determined by the permeability of a porous bed 1 cm high and with a 1 cm² section through which flows a fluid with a viscosity of 1 mPa·s with a flow rate of 1 cm³/sec under an applied pressure differential of 1 atmosphere. The principles for measuring permeability have been previously derived for porous media from Darcy's law (see, for example, J. Bear, “The Equation of Motion of a Homogeneous Fluid: Derivations of Darcy's Law,” in Dynamics of Fluids in Porous Media 161-177 (2nd ed. 1988)). An array of devices and methods are in existence that may correlate with permeability. In one exemplary method useful for measuring permeability, a specially constructed device is designed to form a filter cake on a septum from a suspension of filtration media in water; and the time required for a specified volume of water to flow through a measured thickness of filter cake of known cross-sectional area is measured

In some embodiments, the composite material has a permeability in a range from about 0.5 darcys to about 20 darcys. In some embodiments, the composite material has a permeability in a range from about 0.5 darcys to about 10 darcys. In some embodiments, the composite material has a permeability in a range from about 0.5 darcys to about 5 darcys. In some embodiments, permeability may be in a range from about 0.5 darcys to about 2 darcys. In some embodiments, the permeability may be in a range from about 1 darcy to about 2 darcys.

The composite materials, such as the agglomerated materials, disclosed herein have a particle size. Particle size may be measured by any appropriate measurement technique now known to the skilled artisan or hereafter discovered. In one exemplary method, particle size and particle size properties, such as particle size distribution (“psd”), are measured using a Leeds and Northrup Microtrac X100 laser particle size analyzer (Leeds and Northrup, North Wales, Pa., USA), which can determine particle size distribution over a particle size range from 0.12 μm to 704 μm. The size of a given particle is expressed in terms of the diameter of a sphere of equivalent diameter that sediments through the suspension, also known as an equivalent spherical diameter or “esd.” The median particle size, or d₅₀ value, is the value at which 50% by weight of the particles have an esd less than that d₅₀ value. The d₁₀ value is the value at which 10% by weight of the particles have an esd less than that d₁₀ value. The d₉₀ value is the value at which 90% by weight of the particles have an esd less than that d₉₀ value.

In some embodiments, the d₁₀ of the composite material is in a range from about 5 μm to about 30 μm. In some embodiments, the d₁₀ is in a range from about 10 μm to about 30 μm. In some embodiments, the d₁₀ is in a range from about 15 μm to about 30 μm. In some embodiments, the d₁₀ is in a range from about 20 μm to about 30 μm.

In some embodiments, the d₅₀ of the composite material is in a range from about 15 μm to about 80 μm. In some embodiments, the d₅₀ is in a range from about 20 μm to about 80 μm. In some embodiments, the d₅₀ is in a range from about 30 μm to about 80 μm. In some embodiments, the d₅₀ is in a range from about 40 μm to about 80 μm. In some embodiments, the d₅₀ is in a range from about 50 μm to about 80 μm. In some embodiments, the d₅₀ is in a range from about 60 μm to about 80 μm.

In some embodiments, the d₉₀ of the composite material is in a range from about 50 μm to about 200 μm. In some embodiments, the d₉₀ is in a range from about 60 μm to about 200 μm. In some embodiments, the d₉₀ is in a range from about 70 μm to about 200 μm. In some embodiments, the d₉₀ is in a range from about 80 μm to about 0 μm. In some embodiments, the d₉₀ is in a range from about 90 μm to about 200 μm. In some embodiments, the d₉₀ is in a range from about 100 μm to about 200 μm. In some embodiments, the d₉₀ is in a range from about 110 μm to about 200 μm. In some embodiments, the d₉₀ is in a range from about 120 μm to about 200 μm. In some embodiments, the d₉₀ is in a range from about 150 μm to about 200 μm.

The composite materials disclosed herein may have a low crystalline silica content. Forms of crystalline silica include, but are not limited to, quartz, cristobalite, and tridymite. In some embodiments, the composite material has a lower content of at least one crystalline silica than a composite material not subjected to at least one co-agglomeration with at least one binder.

The composite materials disclosed herein may have a low cristobalite content. Cristobalite content may be measured by any appropriate measurement technique now known to the skilled artisan or hereafter discovered. In one exemplary method, cristobalite content is measured by x-ray diffraction. Cristobalite content may be measured, for example, by the quantitative X-ray diffraction method outlined in H. P. Klug and L. E. Alexander, X-Ray Diffraction Procedures for Polycrystalline and Amorphous Materials 531-563 (2nd ed. 1972), which is incorporated by reference herein in its entirety. According to one example of that method, a sample is milled in a mortar and pestle to a fine powder, then back-loaded into a sample holder. The sample and its holder are placed into the beam path of an X-ray diffraction system and exposed to collimated X-rays using an accelerating voltage of 40 kV and a current of 20 mA focused on a copper target. Diffraction data are acquired by step-scanning over the angular region representing the interplanar spacing within the crystalline lattice structure of cristobalite, yielding the greatest diffracted intensity. That region ranges from 21 to 23 2θ (2-theta), with data collected in 0.05 2θ steps, counted for 20 seconds per step. The net integrated peak intensity is compared with those of standards of cristobalite prepared by the standard additions method in amorphous silica to determine the weight percent of the cristobalite phase in a sample.

In some embodiments, the cristobalite content is less than about 20% by weight. In some embodiments, the cristobalite content is less than about 10% by weight. In some embodiments, the cristobalite content is less than about 6% by weight. In some embodiments, the cristobalite content is less than about 1% by weight. In some embodiments, the composite material has a lower cristobalite content than materials not subjected to co-agglomeration with low extractable metal mineral and a binder.

Composite materials disclosed herein may have a low quartz content. Quartz content may be measured by any appropriate measurement technique now known to the skilled artisan or hereafter discovered. In one exemplary method, quartz content is measured by x-ray diffraction. For example, quartz content may be measured by the same x-ray diffraction method described above for cristobalite content, except the that 20 region ranges from 26.0 to 27.5 degrees. In some embodiments, the quartz content is less than about 0.5%. In some embodiments, the quartz content is less than about 0.25%. In some embodiments, the quartz content is less than about 0.1%. In some embodiments, the quartz content is about 0%, In some embodiments, the quartz content may be in a range from about 0% to about 0.5%. In some embodiments, the quartz content may be in a range from about 0% to about 0.25%.

Composite materials disclosed herein may have a measurable pore volume. Pore volume may be measured by any appropriate measurement technique now known to the skilled artisan or hereafter discovered. In one exemplary method, pore volume is measured with an AutoPore IV 9500 series mercury porosimeter from Micromeritics Instrument Corporation (Norcross, Ga., USA), which can determine measure pore diameters in a range from 0.006 to 600 μm. As used to measure the pore volume of the composite materials disclosed herein, that porosimeter's contact angle was set at 130 degrees, and the pressure ranged from 0 to 33,000 psi. In some embodiments, the pore volume of the composition is about equal to the diatomaceous earth and/or low extractable metal mineral from which it is made. In some embodiments, the pore volume may be in a range from about 1 mL/g to about 10 mL/g. In some embodiments, the pore volume may be in a range from about 4 mL/g to about 8 mL/g. In some embodiments, the pore volume may be in a range from about 4 mL/g to about 6 mL/g. In some embodiments, the pore volume is about 5 mL/g.

Composite materials disclosed herein may have a measurable median pore size. Median pore size may be measured by any appropriate measurement technique now known to the skilled artisan or hereafter discovered. In one exemplary method, median pore size is measured with an AutoPore IV 9500 series mercury porosimeter, as described above. In some embodiments, the median pore size is in a range from about 1 μm to about 10 μm. In some embodiments, the median pore size is in a range from about 2 μm to about 7 μm, In some embodiments, the median pore size is in a range from about 2 μm to about 5 μm.

Composite materials disclosed herein may have a measurable wet density, which as used herein refers to measurement of centrifuged wet density. According to one exemplary method, to measure wet density, a composite material sample of known weight from about 1.00 to about 2.00 g is placed in a calibrated 15 ml centrifuge tube to which deionized water is added to make up a volume of approximately 10 ml. The mixture is shaken thoroughly until all of the sample is wetted, and no powder remains. Additional deionized water is added around the top of the centrifuge tube to rinse down any mixture adhering to the side of the tube from shaking. The tube is centrifuged for 5 minutes at 2500 rpm on an IEC Centra® MP-4R centrifuge, equipped with a Model 221 swinging bucket rotor (International Equipment Company; Needham Heights, Mass., USA). Following centrifugation, the tube is carefully removed without disturbing the solids, and the level (i.e., volume) of the settled matter is measured in cm³. The centrifuged wet density of powder is readily calculated by dividing the sample weight by the measured volume. In some embodiments, the wet density is in a range from about 10 lbs/ft³ to about 20 lbs/ft³. In some embodiments,the wet density is in a range from about 10 lbs/ft³ to about 16 lbs/ft³ or about 12 lbs/ft³ to about 15 lbs/ft³.

Composite materials disclosed herein may include at least one soluble metal. As used herein, the term “soluble metal” refers to any metal that may be dissolved in at least one liquid. Soluble metals are known to those of skill in the art and include, but are not limited to, iron, aluminum, calcium, vanadium, chromium, copper, zinc, nickel, cadmium, and mercury. When a filter aid including a composite material is used to filter at least one liquid, at least one soluble metal may dissociate from the composite material filter aid and enter the liquid. In many applications, such an increase in metal content of the liquid may be undesirable and/or unacceptable. For example, when a filter aid including a composite material is used to filter beer, a high level of iron dissolved in the beer from the filter aid may adversely affect sensory or other properties, including but not limited to taste and shelf-life.

Any appropriate protocol or test for measuring levels of at least one soluble metal in composite materials may be used, including those now known to the skilled artisan or hereafter discovered. For example, the brewing industry has developed at least one protocol to measure the beer soluble iron (BSI) of composite material filter aids. BSI refers to the iron content, which may be measured in parts per million, of a filter aid including an material that dissociates in the presence of a liquid, such as beer. The European Beverage Convention (EBC) method contacts liquid potassium hydrogen phthalate with the filter aid and then analyzes the liquid for iron content. More specifically, the EBC method uses, for example, a 10 g/L solution of potassium hydrogen phthalate (KHP, KHC₈H₄O₄) as the extractant along with a given quantity of filter aid material, with a total contact time of two hours. Extracts are then analyzed for iron concentration by the FERROZINE method.

In some embodiments, the beer soluble iron of the composite material disclosed herein is in a range from less about 1 ppm to about 50 ppm, when measured using the EBC method. In some embodiments, the beer soluble iron is in a range from about 1 ppm to about 40 ppm, from about 1 ppm to about 30 ppm, from about 3 ppm to about 20 ppm. In some embodiments, the beer soluble iron is in a range from about 5 ppm to about 15 ppm. In some embodiments, the beer soluble iron is less than about 13 ppm.

Other beer soluble metals can also be measured using the EBC method, and the extracts may be analyzed for metal concentrations according to methods known in the art.

In some embodiments, the beer soluble aluminum of the composite material disclosed herein is in a range from less about 1 ppm to about 30 ppm, when measured using the EBC method. In some embodiments, the beer soluble aluminum is in a range from about 3 ppm to about 20 ppm. In some embodiments, the beer soluble aluminum is in a range from about 5 ppm to about 15 ppm. In some embodiments, the beer soluble aluminum is less than about 13 ppm.

In some embodiments, the beer soluble arsenic of the composite material disclosed herein is in a range from less about 1 ppm to about 5 ppm, when measured using the EBC method. In some embodiments, the beer soluble arsenic is in a range from about 0.1 ppm to about 2.5 ppm. In some embodiments, the beer soluble arsenic is in a range from about 0.1 ppm to about 1 ppm. In some embodiments, the beer soluble arsenic is less than about 2 ppm.

In some embodiments, the beer soluble calcium of the composite material disclosed herein is in a range from less about 1 ppm to about 200 ppm, when measured using the EBC method. In some embodiments, the beer soluble calcium is in a range from about 5 ppm to about 100 ppm. In some embodiments, the beer soluble calcium is in a range from about 5 ppm to about 50 ppm. In some embodiments, the beer soluble calcium is less than about 30 ppm.

According to some embodiments, the composite filter aid has an acid-soluble iron content of less than 100 mg/kg, as measured by FCC. For example, the filter aid has an acid-soluble iron content of less than 50 mg/kg, less than 40 mg/kg, or less than 30 mg/kg, as measured by FCC. The acid-soluble iron content may be measured according to known methods, such as, for example, FCC 9 of the U.S. Pharmacopeial Convention. According to some embodiments, the composite filter aid has an acid-soluble iron content of less than 100 ppm, as measured by FCC. For example, the filter aid has an acid-soluble iron content of less than 50 ppm, less than 40 ppm, less than 30 ppm, less than 20 ppm, or less than 10 ppm, as measured by FCC.

According to some embodiments, the composite filter aid has an acid-soluble aluminum content of less than 280 mg/kg, as measured by FCC. For example, the filter aid has an acid-soluble aluminum content of less than 200 mg/kg, less than 100 mg/kg, or less than 80 mg/kg, as measured by FCC. According to some embodiments, the composite filter aid has an acid-soluble aluminum content of less than 280 ppm, as measured by FCC. For example, the filter aid has an acid-soluble aluminum content of less than 100 ppm, less than 50 ppm, less than 30 ppm, less than 20 ppm, less than 15 ppm, or less than 10 ppm, as measured by FCC.

According to some embodiments, the composite filter aid has an acid-soluble arsenic content of less than 5 mg/kg, as measured by FCC. For example, the filter aid has an acid-soluble arsenic content of less than 2 mg/kg, less than 1 mg/kg, or less than 0.5 mg/kg, as measured by FCC. According to some embodiments, the composite filter aid has an acid-soluble arsenic content of less than 10 ppm, as measured by FCC. For example, the filter aid has an acid-soluble arsenic content of less than 5 ppm, less than 2 ppm, less than 1 ppm, less than 0.5 ppm, or less than 0.2 ppm, as measured by FCC.

According to some embodiments, the composite filter aid has an acid-soluble calcium content of less than 200 mg/kg, as measured by FCC. For example, the filter aid has an acid-soluble calcium content of less than 150 mg/kg, less than 100 mg/kg, less than 50 mg/ kg, or less than 30 mg/kg, as measured by FCC. According to some embodiments, the composite filter aid has an acid-soluble calcium content of less than 200 ppm, as measured by FCC. For example, the filter aid has an acid-soluble calcium content of less than 150 ppm, less than 100 ppm, less than 50 ppm, or less than 30 ppm, as measured by FCC.

The composite materials disclosed herein may have a measurable BET surface area. BET surface area, as used herein, refers to the technique for calculating specific surface area of physical absorption molecules according to Brunauer, Emmett, and Teller (“BET”) theory. BET surface area may be measured by any appropriate measurement technique now known to the skilled artisan or hereafter discovered. In one exemplary method, BET surface area is measured with a Gemini III 2375 Surface Area Analyzer, using pure nitrogen as the sorbent gas, from Micromeritics Instrument Corporation (Norcross, Ga., USA). In some embodiments, the BET surface area is greater than for an material not produced according to embodiments described herein (e.g., without co-agglomerating diatomaceous earth and low extractable metal mineral with a binder). In some embodiments, the BET surface area is in a range from about 1 m²/g to about 50 m²/g. In some embodiments, the BET surface area is in a range from about 5 m²/g to about 30 m²/g. In some embodiments, the BET surface area is greater than about 10 m²/g. Without wishing to be bound by a particular theory, acid-washing may increase the surface area of the diatomaceous earth and/or low extractable metal mineral.

Exemplary Uses for Composite Materials

The exemplary composite materials, such as the agglomerated acid-washed diatomaceous earth and low extractable metal mineral, disclosed herein may be used in any of a variety of processes, applications, and materials. For example, the composite materials may be used in at least one process, application, or material in which such a product with a high BET surface area is desirable.

For example, the composite materials may be incorporated into a filter aid material or composition. A filter aid composition including at least one composite material may optionally include at least one additional filter aid medium. Examples of suitable additional filter aid media include, but are not limited to, natural or synthetic silicate or aluminosilicate materials, unimproved diatomaceous earth, saltwater diatomaceous earth, expanded perlite, pumicite, natural glass, cellulose, activated charcoal, feldspars, nepheline syenite, sepiolite, zeolite, and clay.

The at least one additional filter medium may be present in any appropriate amount. For example, the at least one additional filter medium may be present from about 0.01 to about 100 parts of at least one additional filter medium per part of the composite material. In some embodiments, the at least one additional filter medium is present from about 0.1 to about 10 parts. In some embodiments, the at least one additional filter medium is present from about 0.5 to 5 parts.

The filter aid composition may be formed into sheets, pads, cartridges, or other monolithic or aggregate media capable of being used as supports or substrates in a filter process. Considerations in the manufacture of filter aid compositions may include a variety of parameters, including but not limited to total soluble metal content of the composition, median soluble metal content of the composition, particle size distribution, pore size, cost, and availability.

A filter aid composition including at least one composite material may be used in a variety of processes and compositions. In some embodiments, the filter aid composition is applied to a filter septum to protect it and/or to improve clarity of the liquid to be filtered in a filtration process. In some embodiments, the filter aid composition is added directly to a beverage to be filtered to increase flow rate and/or extend the filtration cycle. In some embodiments, the filter aid composition is used as pre-coating, in body feeding, or a combination of both pre-coating and body feeding, in a filtration process.

Embodiments of the composite material may also be used in a variety of filtering methods. In some embodiments, the filtering method includes pre-coating at least one filter element with at least one composite material, and contacting at least one liquid to be filtered with the at least one coated filter element. In such embodiments, the contacting may include passing the liquid through the filter element. In some embodiments, the filtering method includes suspending at least one composite material filter aid in at least one liquid containing particles to be removed from the liquid, and thereafter separating the filter aid from the filtered liquid.

Filter aids including at least one composite material disclosed herein may also be employed to filter various types of liquids. In some embodiments, the liquid is a beverage. Exemplary beverages include, but are not limited to, vegetable-based juices, fruit juices, distilled spirits, and malt-based liquids. Exemplary malt-based liquids include, but are not limited to, beer and wine. In some embodiments, the liquid is one that tends to form haze upon chilling. In some embodiments, the liquid is a beverage that tends to form haze upon chilling. In some embodiments, the liquid is a beer. In some embodiments, the liquid is an oil. In some embodiments, the liquid is an edible oil. In some embodiments, the liquid is a fuel oil. In some embodiments, the liquid is water, including but not limited to waste water. In some embodiments, the liquid is blood. In some embodiments, the liquid is a sake. In some embodiments, the liquid is a sweetener, such as, for example, corn syrup or molasses.

The composite materials disclosed herein may also be used in applications other than filtration. In some embodiments, the composite materials may be used as composites in filler applications, such as, for example, fillers in construction or building materials. In some embodiments, the composite materials may be used to alter the appearance and/or properties of paints, enamels, lacquers, or related coatings and finishes. In some embodiments, the composite materials may be used in paper formulations and/or paper processing applications. In some embodiments, the composite materials may be used to provide anti-block and/or reinforcing properties to polymers. In some embodiments, the composite materials may be used as or in abrasives. In some embodiments, the composite materials may be used for buffing or in buffing compositions. In some embodiments, the composite materials may be used for polishing or in polishing compositions. In some embodiments, the composite materials may be used in the processing and/or preparation of catalysts. In some embodiments, the composite materials may be used as chromatographic supports or other support media. In some embodiments, the composite materials may be blended, mixed, or otherwise combined with other ingredients to make monolithic or aggregate media useful in a variety of applications, including but not limited to supports (e.g., for microbe immobilization) and substrates (e.g., for enzyme immobilization).

EXAMPLES

Several examples consistent with the composite materials disclosed herein are described below. The compositions of the examples are provided in Table 1.

For the examples, a commercially available diatomite product Standard Super-Cel was used as the diatomaceous earth feed material. This diatomaceous earth feed material had a particle size distribution having a d₁₀ of 5.9 microns, a d₅₀ of 20.7 microns, and d₉₀ of 65.3 microns. A commercially available, expanded and milled perlite product was used as the low extractable metal mineral feed material in some examples, and an acid-washed form of the same perlite was used on other examples, as shown in Table 1 below. The perlite mineral feed material had a particle size distribution having a d₁₀ of 3 microns, a d₅₀ of 8 microns, and a d₉₀ of 20 microns. One kg of DE (Standard Super-Cel®) or one kg of perlite (Harborlite 400®) slurry was prepared with 0.15N sulfuric acid at 15% solids concentration. After mixing for 2 hours at room temperature, the slurry was then filtered through #4 paper filter paper using a Büchner funnel. The filter cake was rinsed with DI water until the conductivity of the filtrate is less than 10 uS. The rinsed filter cake was then dried in the oven at 150 C and then brushed through a 30 mesh sieve.

The acid washed diatomite product Celite® Standard Super-Cell® (AW SSC) from Lompoc was used as the DE feed material. An expanded and milled perlite product Harborlite 400® (H400) or the acid-washed Harborlite 400® (AW H400) was used as the perlite feed material. A binder was prepared by dispersing 2.5 grams of sodium silicate in 10 grams of deionized water, and was then slowly added to 50 grams of a mixture of the diatomaceous earth feed material and the low extractable metal mineral feed material in a Hobart® food mixer. The same amount of sodium silicate solution was used for all the mixtures of diatomaceous earth feed material and the low extractable metal mineral feed material with different ratios. After mixing in for 15 minutes, the mixture of sodium silicate solution, diatomaceous earth feed material, and low extractable metal mineral feed material was brushed through a 14 mesh screen with 1.41 millimeter openings. The oversize particles were broken and forced through the screen by brushing. After drying in a 150° C. oven overnight, the material was brushed through a 30 mesh screen with 0.6 millimeter openings.

The weight of sodium silicate and water in Table 1 is relative to the weight of combined diatomaceous earth feed material and low extractable metal feed material. A non-acid-washed, flux-calcined diatomaceous earth, commercially available as Celite® Hyflo®, was used as a control.

TABLE 1 Acid Wash Acid Wash Sodium DE Perlite Perlite Silicate Water Examples (%) (%) (%) (%) (%) Control (Hyflo) 0 0 0 5 20 Example 1 50 50 0 5 20 Example 2 25 75 0 5 20 Example 3 75 25 0 5 20 Example 4 50 0 50 5 20 Example 5 25 0 75 5 20 Example 6 75 0 25 5 20

Permeability, porosity, pore volume, and median pore size of the control and example materials was measured. Permeability was measured using the method mentioned earlier derived from Darcy's law (e.g., according to J. Bear). Porosity, pore volume, and median pore size were measured using an AutoPore IV 9500® series mercury porosimeter from Micromeritics Instrument Corporation (Norcross, Ga., USA). The results of these measurements are shown in Table 2.

TABLE 2 Wet Pore Median Permeability Density Volume Pore Size Examples (Darcy) (lb/ft²) (mL/g) (μm) Control (Hyflo) 1.04 22.5 2.6972 3.4846 Example 1 0.87 14.5 3.4658 5.4293 Example 2 0.91 13.9 4.6383 3.0606 Example 3 0.88 14.7 3.6085 4.0716 Example 4 1.10 13.9 4.9010 3.4799 Example 5 1.31 13.4 5.5477 4.0376 Example 6 1.18 14.3 4.6138 3.2210

As shown in Table 2, Examples 1-6 have comparable permeability to commercially available diatomaceous earth control material, while also having lower wet densities and larger pore volumes. Median pore size was generally comparable or larger for Examples 1-6 as compared to commercially available diatomaceous earth control material.

The metal content of the control and each of the example materials was measured using the FCC method, the results of which are shown in Table 3 below.

TABLE 3 FCC Al FCC As FCC Ca FCC Cu FCC Pb FCC Fe Examples (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) Control (Hyflo) 282.9 1.0 1168.8 1.3 <0.5 102.9 Example 1 209.6 0.8 80.5 3.7 0.1 94.7 Example 2 249.5 0.4 83.9 1.8 0.2 98.4 Example 3 93.7 0.5 49.6 1.9 0.2 97.1 Example 4 98.4 <0.5 42.3 1.2 <0.5 35.4 Example 5 74.8 <0.5 33.7 0.8 <0.5 31.5 Example 6 73.7 <0.5 33.8 1.3 <0.5 42.7

As shown in Table 3, Examples 1-6 have generally comparable or lower levels of FCC aluminum, arsenic, calcium, and iron than commercially available diatomaceous earth. Examples 4-6 also have comparable or lower levels of FCC copper than commercially available diatomaceous earth.

Soluble metal contents of each of the control and examples was measured using the EBC method, the results of which are shown in Table 4 below.

TABLE 4 EBC Al EBC As EBC Ca EBC Fe Examples (ppm) (ppm) (ppm) (ppm) Control (Hyflo) 5.0 <2 213.7 49.2 Example 1 23.5 0.4 32.4 11.4 Example 2 29.3 0.1 38.4 12.7 Example 3 11.1 2.3 26.9 13.8 Example 4 15.8 <2 25.4 9.6 Example 5 10.2 <2 13.7 7.4 Example 6 6.6 <2 10.8 11.7

As shown in Table 4, the example composites have lower beer soluble iron and calcium than commercially available diatomaceous earth. The example composites also have similar or lower beer soluble arsenic as compared to commercially available diatomaceous earth.

FIGS. 1-4 are graphs depicting pressure versus filtration time and turbidity versus filtration time, respectively, for two exemplary filter aids (Examples 1 and 4) as compared to the control. The pressure and turbidity were measured with 2 grams of precoated material forming the filter cake. Water with 5 g/L. Ovaltine was filtered at a flow ate of 124 ml/min, with a body feed of 2 g/L of either the control or example filter aid as the feed. The example filter aids were also tests at 75% of the body feed (i.e., 1.5 g/L).

As shown in FIG. 1, the filter aid of commercially available diatomaceous earth (DE) resulted in the highest pressure. The filter aid of Example 1 (acid-washed diatomaceous earth and perlite agglomerates) had a much lower pressure than the commercial diatomaceous earth, and the filter aid of Example 1 at 75% bodyfeed had the pressure higher than Example 1 at 100% bodyfeed and slightly lower than the commercial DE product.

As shown in FIG. 2, turbidity versus time for Example 1 as compared to the control shows that Example 1 had a slightly higher initial turbidity, but stabilized to a turbidity similar to the commercially available diatomaceous earth over time.

As shown in FIG. 3, the filter aid of commercially available diatomaceous earth (DE) resulted in the highest pressure. The filter aid of Example 4 (acid-washed diatomaceous earth and acid-washed perlite agglomerates) had a much lower pressure than the commercial diatomaceous earth, and the filter aid of Example 4 at 75% bodyfeed had the pressure higher than Example 4 at 100% bodyfeed and slightly lower than the commercial DE product.

As shown in FIG. 4, turbidity versus time for Example 4 as compared to the control shows that Example 4 has a higher initial turbidity, but stabilized to a turbidity similar to the commercially available diatomaceous earth over time.

The tests of FIGS. 1-4 indicate that filtration performance of a filter aid having acid-washed diatomaceous earth and low extractable metal mineral is better than commercially available diatomaceous earth with a lower pressure rise. As also shown in FIGS. 1-4, the body feed of the exemplary filter aids can be reduced by 25% without negatively impacting performance.

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims. 

1. A composite filter aid comprising: an acid-washed diatomaceous earth: and a low extractable metal mineral,
 2. The composite filter aid of claim 1, wherein the composite filter aid comprises an agglomerated composite filter aid including the acid-washed diatomaceous earth and the low extractable metal mineral.
 3. The composite filter aid of claim 1, wherein the filter aid has a permeability in a range from 0.1 to 20 darcys.
 4. (canceled)
 5. The composite filter aid of claim 1, wherein the low extractable metal mineral is perlite.
 6. The composite filter aid of claim 5, wherein the perlite comprises an expanded perlite.
 7. The composite filter aid of claim 5, wherein the perlite comprises an unexpanded perlite.
 8. The composite filter aid of claim 5, wherein the perlite comprises a milled expanded perlite.
 9. (canceled)
 10. The composite filter aid of claim 1, wherein the low extractable metal mineral has a low soluble metal content with FCC arsenic less than 0.5 mg/kg and BBC iron less than 30 mg/kg. 11-15. (canceled)
 16. The composite filter aid of claim 1, further comprising a binder.
 17. (canceled)
 18. The composite filter aid of claim 16, wherein the binder comprises an alkali silicate binder.
 19. The composite filter aid of claim 16, wherein the binder is selected from the group consisting of a cellulose, polyethylene glycol (PEG), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), starch, Candalilla wax, a polyacrylate or related copolymer, a polydiallyldimethylammonium chloride polymer or copolymer, dextrin, lignosulfonate, sodium alginate, magnesium stearate, a silica binder, an alkali silica, or mixtures thereof. 20-21. (canceled)
 22. The composite filter aid of claim 1, wherein the filter aid has a d₅₀ in a range from 30 to 70 microns. 23-30. (canceled)
 31. The composite filter aid of claim 1, wherein the filter aid has a BET surface area in a range from 5 m²/g to about 50 m²/g.
 32. The composite filter aid of claim 1, wherein the composite filter aid has a median pore size in a range from 1 to 35 microns.
 33. The composite filter aid of claim 1, wherein the porosity of the composite filter aid is in a range from 2 to 7 mL/g.
 34. The composite filter aid of claim 1, wherein the filter aid has a beer soluble iron content of less than 40 ppm, as measured by EBC.
 35. The composite filter aid of claim 1, wherein the composite filter aid has a cristobalite content of less than 20% by weight.
 36. The composite filter aid of claim 1, wherein the composite filter aid has a wet density in a range from 5 to 20 lbs/ft³.
 37. A method for making a composite material, the method comprising: blending an acid-washed diatomaceous earth and a low extractable metal mineral; adding a binder to the blended diatomaceous earth and low extractable metal mineral; and forming the composite material from the acid-washed diatomaceous earth, the low extractable metal mineral, and the binder. 38-49. (canceled)
 50. A method for filtering a liquid, the method comprising: providing a liquid for filtering; and filtering the liquid through a composite filter aid comprising an acid-washed diatomaceous earth, and a low extractable metal mineral. 51-54. (canceled) 